1. Field of the Invention
This invention relates generally to microchannel pressure vessels. Specifically, this invention relates to maximum allowable working pressure determination and pressure vessel certification of diffusion-bonded microchannel heat exchangers and microchannel heat exchanger/reactor combinations operating at higher temperatures.
2. Description of Related Art
Pressure vessel certification organizations, such as the American Society of Mechanical Engineers (ASME), establish rules of safety governing the design, fabrication, and inspection of boilers and pressure vessels. Other pressure vessel certification organizations include the European Commission through its Pressure Equipment Directive (PED), the Japanese Industrial Standards Committee which coordinates the standardization process of creating the Japanese Industrial Standards (JIS) which are then published by the Japanese Standards Association, and the International Organization for Standardization (ISO) which is developing ISO 16528. For example, the International Boiler and Pressure Vessel Code, published by the ASME, provides the procedures to follow to become accredited to certify products comply with the Code. Accreditation packages include the use of, for example, ASME Code Symbol Stamps such as the so-called “U” stamp for pressure vessels. To meet the requirements of the Code, the strength of the vessel may be computed based upon established formulas or hydrostatic tests which determine the maximum allowable working pressure (MAWP).
Many factors must be considered in MAWP determinations, such as the basic materials of construction (e.g., 10xx carbon steel, type 316L stainless as well as other steels, nickel alloy 617 as well as other nickel alloys, aluminum, titanium, platinum, rhodium, copper, chromium, brass, alloys of the foregoing materials, polymers; such as thermoset resins, ceramics, glass, polymer/fiberglass composites, quartz, silicon, or combinations thereof), methods of preparing construction components (e.g., stamping, photochemical etching or machining, electrodischarge machining, laser cutting, drilling and milling), methods of joining (e.g., welding, brazing, diffusion bonding, soldering, and adhesives), the design and various cross-sections of the vessel, the pressure and temperature regimes experienced by the vessel, not only during normal operating conditions, but during startup and shutdown, and the presence or absence of spurious artifacts.
When the MAWP cannot be satisfactorily determined using established methods, however, especially when employing non-traditional materials of construction, when higher temperatures are expected, particularly when those higher temperatures may cause significant creep, when non-traditional fabrication or joining methods are used, and, more particularly, when spurious artifacts arise, other methods must be employed. There exists then, a need for a method to determine MAWP and meet certification standards when employing higher temperatures, particularly when creep may be significant, when using non-traditional materials of construction, non-traditional component fabrication and joining methods, when fabrication-related artifacts arise, or combinations thereof.